#include<stdio.h>
int main()
{
	int i=1;
	double sum=0;
	for(i=1;i<=100;i++)
	{
		if(i%2!=0)
		{
			sum=sum+1.0/i;
		}
		else
		{
			sum=sum-1.0/i;
		}
		
	}
	printf("%lf\n",sum);	
	return 0;
} 
